ERBB2 and metastasis: The various BCSs had site-specific metastasis patterns, patients with HR+/HER2+ and HR−/HER2+ subtypes were prone to abdominal/pelvic metastasis, patients with HR+/HER2− and HR+/HER2+ subtypes were prone to bone metastasis, while patients with the HR−/HER2− subtype were prone to lung/mediastinal and brain metastases.